Photo timer

ABSTRACT

A phototimer for controlling a radiographic exposure includes a plurality of light transmitting panels each having a light accepting portion adjacent a separate area of fluorescent screen. The light transmitting panels have light emitting portions positioned adjacent a light responsive phototube. Movable shielding means selectively block the transmission of the light from the light transmitting panels to the phototube whereby light from selected portions of the fluorescent screen may be transmitted to the light responsive phototube.

United States Patent 1191 Slagle PHOTO TIMER [75] Inventor: Edward Slagle, Lyndhurst, Ohio [73] Assignee: Picker Corporation, Cleveland, Ohio [22] Filed: June 28, 1971 [21] Appl. No.:'l57,536

52 US. Cl. 250/660, 250/483, 250/508 51 1m. (:1 H05 1/38 [58] Field of Search 250/65, 95, 227, 250/219 F, 86; 350/96 [56] References Cited UNITED STATES PATENTS 2,993,123 7/1961 Ball 250/95 2,943,198 6/1960 Godbarsen 250/9s 2,503,062 4/1950 Moriarity 250 3,628,035 12/1971 Olsson 250/ 2,840,716 6/1958 Godbarsen 250 9s 2,695,964 11 1954 Schepker 250/95 Aug. 14, 1973 3,444,378 5/1969 Cibula .Q ..250/9s 2,441,324 5/1943 Morgan ..250/95 2,901,632

8/1959 Stava 250/95 Primary Examiner-James W. Lawrence Assistant Examiner-D. C. Nelms At:orney-Watts, Hoffman, Fisher & l-leinke [57] ABSTRACT A phototimer for controlling a radiographic exposure includes a plurality of light transmitting panels each having a light accepting portion adjacent a separate area of fluorescent screen. The light transmitting panels have light emitting portions positioned adjacent a light responsive phototube. Movable shielding means selectively block the transmission of the light from the light transmittin anels to the phototube whereby light from selected p cm of the fluorescent screen may be transmitted to the light responsive phototube.

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INVENTOR. EDWAR D S LAGLE BY wwwfiia/fih ATTORN EYS PHOTO TIMER CROSS-REFERENCE TO RELATED PATENTS X-RAY TIMING DEVICE USING A LIGHT- CONDUCTING PADDLE WITH SPACED LIGHT- ADMI'ITING HOLES FOR UNINTERRUPT ED LIGHT TRANSMISSION TO A DETECTOR, US. Pat. No. 3,444,378, issued May 13, 1968 to W. G. Cibula et al.

EDGELIGHTED PHOTOTIMER, US. Pat. No. 2,993,123 issued July 18, 1961 to J. C. Ball.

PHOTOELECTRIC TIMER FOR X-RAY APPARA- TUS, US. Pat. No. 2,541,187 issued Feb. 13, 1951 to J. Ball et al.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to X-ray apparatus and more particularly to a means for the phototiming of exposures to X-ray radiation.

2. Prior Art Automatic phototimers of the type having a fluorescent screen positioned behind or beneath a subject in the path of an X-ray beam together with a phototube which receives the light from the screen are well known. A phototimer which employs a plurality of light transmitting panels disposed adjacent separate areas of an fluorescent screen and having a plurality of photoelectric tubes associated with the light transmitting panels is shown in the referenced Ball patent. A suitable control circuit incorporating such photoelectric cells is shown inthe referenced Ball patent. A suitable control circuit incorporating such photoelectric cells is shown in the referenced Ball et al patent where a condenser is connected to receive current from the photoelectric tubes. When the charge on the condenser reaches a critical value it becomes conductive and operates a relay which interrupts the X-ray beam exposure.

It is desirable in controlling the taking of certain types of X-ray photographs to average the light from selected areas of the X-ray photograph. In taking an anterior-posterior exposure of the chest, for instance, it is desirable to average the light received from the right and left chest cavities. Such averaging will prevent improper exposure in the event that one of the chest cavities is substantially congested. It is also desirable to not sample light in the area of the backbone as the light in this area will be substantially lessthan in the regions of the chest cavities, and will cause an improper exposure of the chest cavity regions.

One drawback of known phototimers which provide for the sampling of light from a plurality of selected areas, is that the light from each sampled area is fed to a separate phototube. Hence a plurality of phototubes must be provided as well as circuitry to switch one or more of the phototubes in or out of the control circuit depending on which portions of the screen are in use. Such switching circuitry and the provision of more than one phototube adds considerably to the cost of the phototimer.

Another drawback of known phototimers is that they are too thick to conveniently position them beneath the X-ray table above a Bucky assembly. It is desirable to position the phototimer above the Bucky as film cassettes supported by the Bucky tend to vary in the degree to which they pass or filter X-rays. Such variance between cassettes causes the phototimer to expose some X-ray films for longer periods of time than others.

SUMMARY OF THE PRESENT INVENTION The present invention overcomes the foregoing drawbacks of the prior art and provides a phototimer employing a single light responsive electrical control such as a phototube which may be activated by light from one or more selected regions of an intensifier screen.

A plurality of light transmitting panels are positioned to accept light from separate areas of an intensifier screen. The panels each have a light emitting portion positioned adjacent the phototube. A movable shutter arrangement is provided to selectively block the transmission of light from selected ones of the light emitting portions. Light from one or more selected portions of the intensifier screen may thereby be transmitted to the phototube.

Adjustable light attenuators are provided between the light emitting portions and the phototube to equalize the output effect of each of the light emitting positions. By thisarrangement, an equal illumination of all areas of the fluorescent screen will cause the phototube to receive an equal amount of light from each of the light emitting portions.

Phototimers may be constructed in accordance with the present invention in a sufficiently thin arrangement as to enable them to be positioned above existing Bucky assemblies. Such positioning overcomes the variations in exposure times which result when the phototimer is used beneath cassettes which pass or filter X-rays to different degrees.

Accordingly, it is the principal object of the present invention to provide an improved multiple field phototimer employing a single light responsive device.

Other objects and a fuller understanding of the invention may be had by referring to the following description and claims taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view of an X-ray apparatus with the improved phototimer device of the present invention shown mounted beneath an examination table within the path of X-rays which have passed through a subject and through an X-ray;

FIG. 2 is a sectional view as seen from the plane indicated by the line. 2--2in FIG. 1;

FIG. 3 is an exploded end view of one assembly portion of the device of the present invention;

FIG. 4 is a plan view of the juxtaposed light transmitting panels used in the assembly of FIG. 3;

FIG. 5 is an enlarged end view as seen from the plane indicated by the line 5-5 in FIG. 4;

FIG. 6 is a plan view of the assembly of FIG. 3 with portions thereof broken away to illustrate details;

FIG. 7 is a sectional view as seen from the plane indicated by the line 77 in FIG. 6;

FIG. 8 is a plan view of a light attenuation means which may be employed in the assembly of FIG. 3 or FIG. 9;

FIG. 9 is a schematic illustration showing the light emitting portions of the panels and. their positioning adjacent the light responsive electrical control means;

FIG. 10 is an enlarged plan view of one portion of the phototimer device as shown in FIG. 2;

FIG. 11 is an end view of the apparatus as shown in FIG. and

FIG. 12 is an elevational view of the apparatus of FIG. 10.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings and initially to FIG. 1, an X-ray apparatus is shown generally at 10. The apparatus includes an X-ray tube, not shown, mounted within a protective tube housing 11. The tube and its housing 11 are supported in an operative position by a suitable supporting structure 12.

A subject supporting table 13 is disposed beneath the tube housing 11. The position of a subject to be examined is indicated in broken lines generally at 14. The X-ray tube emits X-rays in a beam emanating from a focal spot shown schematically at 15 and directed toward the subject 14 positioned on the table 13.

A Bucky assembly 16 is positioned beneath the table 13. The Bucky assembly 16 is equipped with the usual reciprocable grid 17 and a cassette or film tray 18. An X-ray sensitive film 19 is positioned within the film tray 18 such that X-rays passing through the subject 14 will cast a shadow which is recorded by the film 19.

A phototimer housing 20 is secured to the top and one side of the Bucky assembly 16. Referring to FIG. 2, the phototimer housing 20 defines first and second adjacent compartments 21, 22. The first compartment 21 houses a suitable light responsive electrical control element such as a phototube 23. The second compartment 22 houses a light emitting assembly 24 which, as will be explained in greater detail, includes an fluorescent screen and a plurality of panels which transmit light to the phototube 23.

Referring to FIG. 3, the construction of the assembly 24 is more clearly shown in an exploded end view. A paddle structure 25 is positioned centrally of the assembly 24 and comprises a plurality of juxtaposed panels as will be explained. The paddle structure 25 along with a paddle mask 26 and an intensifier screen 27 are sandwiched between upper and lower cover plates 28, 29. The cover plate 28 is referred to as the upper cover plate in that it is positioned facing upwardly adjacent the Buckey tray 16. A frame assembly 30 receives and surrounds the sandwiched assembly 24.

The details of the paddle structure 25 are more clearly shown in FIGS. 4 and 5. The paddle structure comprises three juxtaposed light transmitting panels 31, 32, 33. The panels 31, 32, 33 are formed of transparent material of a high refractive index such as synthetic plastic methyl methacrylate, one form of which is known as Lucite. This material has the characteristic that light received within any portion of the panel is transmitted to the edges of the panel. The present invention utilizes this characteristic of the material Lucite to transmit light from light receiving portions 34, 35, 36 to light emitting panel tongue portions 37, 38, 39.

The panels 31, 32 have abutting edges 41, 42. The panels 32, 33 have abutting edges 43, 44. In order to prevent the transmission of light between the panels 31, 32, 33, the abutting edges 41, 42, 43, 44 are beveled as shown in FIG. 5. By beveling the edges as shown, the joint will not cast an X-ray shadow while light traveling through one of the panels toward one of the abutting edges tends to be reflected back into that panel. The

abutting panel edges are also coated with white paint or reflective aluminum tape to further assure that light from one panel will not be transmitted to another panel. The perimetral edges 45-53 of the paddle assembly are also coated with white paint or reflective aluminum tape to further preserve the integrity of light signals received within the individual panels.

Referring to FIGS. 6 and 7, the sandwich assembly 24 is shown as viewed from below with the components broken away to illustrate the details of assembly. The upper and lower covers 28, 29 comprise sheets of opaque fiberboard which are black in color to absorb light. The fluorescent screen 27 comprises a fluorescent sheet which emits visible light when exposed to X- rays. The mask 26 comprises a sheet of opaque fiberboard or paper which is preferably black in color to abosrb light. Rectangular openings 54, 55, 56 are formed through the mask 26 adjacent the light receiving portions 34, 35, 36 of the panels 31, 32, 33. The mask 26 thereby serves to limit the transmission of light from the fluorescent screen 27 to that which passes through the openings 54, 55, 56.

The panels 31, 32, 33 serve to collect the light passing through the mask openings 54, 55, 56 and transmit it to their respective light emitting tongue portions 37, 38, 39. In order to improve the light collection efficiency of the panels 31, 32, 33 the surfaces of the panels opposite the mask openings 54, 55, 56 are coated with rectangular areas of reflective white paint as indicated by the broken lines 57, 58, 59 in FIGS. 4 and 6. These coatings 57, 58, 59 are deposited directly on the panels 31, 32, 33 on the sides adjacent the upper cover 28. By this arrangement, light passing through the panels 31, 32, 33 from the fluorescent screen 27 is diffused and reflected back into the panels.

The light emitting portions 37, 38, 39 receive light indirectly from the light receiving portions 34, 35, 36 as previously described. As will be realized light which enters the panels 31, 32, 33 near the light emittting portions 37, 38, 39 will produce a more intense light signal in the portions 37, 38, 39 than light which enters farther from the portions 37, 38, 39.

It is therefore necessary to provide a light attenuation means to equalize the output effect of all light entering the light receiving portions 34, 35, 36. For this purpose, a light attenuation screen having openings which increase in size from one side to another may be used to attenuate the light passing from the fluorescent screen 27 to the panels 31, 32, 33. Such an attenuation screen is shown generally at 60 in FIG. 8. The attenuation screens 60 are secured to the fluorescent screen 27 on the side adjacent the mask 26 with the smaller openings nearer the portions 37, 38, 39 so as to attenuate the light passing from the screen 27 to the portions 34, 35, 36.

The phototube structure 23 isbest illustrated in FIG. 9. A photoelectric tube 61 is supported at its base end by a tube socket 62. The base end of the tube 61 and the tube socket are housed in a protective casing 63. The light sensitive end of the tube 61 is shielded by an opaque housing 64. The housing 64 has three apertures 65, 66, 67 formed therethrough adjacent the panel light emitting portions 37, 38, 39.

In order for light to pass from the panel portions 37, 38, 39 to the phototube 61, it .must pass through the openings 65, 66, 67. Openings 65, 66, 67 have shutters 68, 69, 70 associated therewith as shown in FIG. 10.

The shutters 68, 69, 70 each comprise a flexible strip of film which isopaque at one end and transparent at the other.

Springs 71, 72, 73 engage the transparent ends of the shutters 68, 69, 70 and serve to bias the shutters toward their closed positions with the opaque ends overlying the openings 65, 66, 67. Flexible cables 74, 75, 76 connect at one end with the opaque ends of the shutters 68, 69, 70 as seen in FIG. 11. The other ends of the cables 74, 75, 76 connect with solenoids 77, 78, 79. By selective energization of the solenoids, any combination of one or more of the shutters 68, 69, 70 may be opened. When the solenoids 77, 78, 79 are de-energized, the springs 71, 72, 73 return the shutters 68, 69, 70 to their closed positions. The housing 64 is teflon coated in the area of movement of the shutters to assure their easy movement and to prevent their becoming scratched.

Referring to FIG. 9, the light-sensitive end of the phototube 61 comprises a tubular glass envelope 80. A pair of annular collars 81, 82 are secured to the glass envelope 80 adjacent opposite ends thereof. Positioned intermediate the collars 81, 82 are three annular light attenuating rings 83, 84, 85. The rings 83, 84, 85 fit snugly about the glass envelope 80 but are rotatable relative to the envelope. The rings 83, 84, 85 comprise strips of flexible film having an opaque area and a transparent area. The opaque area of each ring comprises a V-shaped pattern. In an alternative embodiment, instead of the V-shaped pattern, a light attenua' tion screen of the type shown in FIG. 8 may be formed on the rings 83, 84, 85.

By rotating the rings, 83, 84, 85 relative to the envelope 80, differing amounts of opaque area may be interposed between the panel portions 37, 38, 39 and the phototube 61. The rings 83, 84, 85 thereby provide a means of factory adjustment for balancing the amounts of light receivedby the phototube 61 from the portions 37, 38, 39 when the portions 34, 35, 36 are exposed to equal amounts of light.

An averaging circuit, not shown, is used to average the output of the phototube 61 when two or more of the shutters 68, 69, 70 are opened for exposure. When only one of the shutters 68, 69, 70 is opened for exposure,.the averaging circuit is disconnected and the output of the phototube 61 is fed directly to a suitable phototiming control circuit for controlling the X-ray beam.

In operation, the phototime housing is positioned above the Bucky tray 16 as shown in FIG. 1. Depending upon the characteristics of the subject to be X-rayed, either one or a combination of the phototimer panel regions 31, 32 or 33 are selected for use by the phototiming control. Accordingly, solenoids 77, 78, 79 are appropriately energized or de-energized to open or close shutters 68, 69, 70. At the same time, the above mentioned averaging circuit is connected or disconnected in series with the output of the phototube 61. The signal fed to the X-ray beam control circuit is then representative of the exposure of the film 19 within the Bucky tray 16.

Although the invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from thespirit and the scope of the invention as hereinafter claimed.

What is claimed is:

1. A device for use in combination with a light responsive electrical signal generating means coupled to an electrical control system for controlling an X-ray beam from an X-ray tube source, comprising:

a. a fluorescent screen for transforming X-rays into visible light;

b. a plurality of light transmitting panels each having light accepting portions adjacent separate areas of said fluorescent screen and having light emitting portions positioned adjacent the light responsive means for transmitting light to the light responsive means; and

c. movable shielding means for selectively blocking the transmission of light from at least one of said light emitting portions to said light responsive means;

d. whereby light from selected portions of said fluorescent screen may be transmitted to the light responsive electrical control means.

2. The device of claim 1 wherein said movable shielding means comprises a separate shield for blocking the transmission of light from each one of said light emittting portions to the light responsive means.

3. The device of claim 2 additionally including shield positioning means for selectively positioning each of said shields to control the transmission of light from said light emitting portions to the light responsive means.

4. A device for use in combination with an electrical control system including a light responsive signal generating means for controlling an X-ray beam from an X-ray tube source, comprising:

a. a fluorescent screen for transforming X-rays into visible light;

b. three juxtaposed light transmitting panels each having a light accepting portion adjacent a separate area of said fluorescent screen and having a light emitting portion positioned adjacent the light responsive means for transmitting light to the light responsivemeans; a

c. movable shielding means for selectively blocking the transmission of light from said light emitting portions to the light responsive means and,

d. shield positioning means for selectively positioning said movable shielding means.

5. The device of claim 4 wherein said movable shielding means includes three shields each adapted to selectively block the transmission of light from a separate one of said light emitting portions to the light responsive means.

6. The device of claim 5 additionally including adjustable light attenuation means positioned between said light emitting portions and the light responsive means for equalizing the output effect of each of said light emitting portions.

7. A device for use in combination with a light responsive electrical signal generating; means coupled to an electrical control system for controlling an X-ray beam from an X-ray tube source, comprising a. a fluorescent screen for transforming X-rays into visible light; j

b. a plurality of light transmitting panels each having at least one light accepting portion adjacent a separate area of said fluorescent screen and having a light emitting portion adjacent the light responsive means for transmitting light to the light responsive means;

c. movable shielding means for selectively blocking the transmission of light from said light emitting portions to the light responsive means;

d.-shield positioning means for selectively positioning said movable shielding means; and,

e. light attenuation means adapted to equalize the output effect of each of said light emitting portions.

8. The device of claim 7 additionally including:

a. cover means adapted to shield said light transmitting panels such that the only light received by said panels is light emanating from said fluorescent screen; and,

b. masking means positioned between said fluorescent screen and said light transmitting panels to limit the transmission of light therebetween to the area of said light accepting portions.

9. The device of claim 8 wherein said cover means includes:

a. a first light-shielding cover positioned adjacent said light receiving panels on the side opposite said masking means;

b. a second light-shielding cover positioned adjacent said fluorescent screen on the side opposite said masking means; and,

c. a light-shielding peripheral enclosure receiving said first and second covers with said fluorescent screen, said masking means, and said panels sandwiched therebetween.

10. A device for use in combination with a light responsive electrical signal generating means coupled to an electrical control system for controlling an X-ray beam from an X-ray tube source, comprising:

a. an X-ray responsive light generating assembly positioned within the beam of X-rays comprising a fluorescent screen for transforming X-rays into visible light and plurality of light transmitting panels each having at least one light accepting portion adjacent a separate area of said fluorescent screen and having a light emitting portion adjacent the light responsive means for transmitting light to the light responsive means;

b. said assembly including masking means positioned between said fluorescent screen and said light transmitting panels to limit the transmission of light therebetween to the area of said light accepting portions;

c. movable shielding means for selectively blocking the transmission of light from said light emitting portions to the light responsive means;

d. shield positioning means for selectively positioning said movable shielding means; and,

e. light attenuation means adapted to equalize the output effect of each of said light emitting portions.

11. The device of claim 10 wherein said light transmitting panels comprise three panels having abutting edge portions juxtaposed so as to form a contiguous surface, and an opaque substance is interposed between said abutting edge portions to prevent the transmission of light between said panels.

12. The device of claim 10 wherein said movable shielding means comprises a. a housing surrounding said light responsive electrical control mean, said housing having at least one opening therethrough adjacent said light emitting protions; and

b. a plurality of movable shutter means adapted to control the transmission of light from said light emitting portions through said opening to the light responsive means.

13. The device of claim 12 wherein said shield positioning means comprises a plurality of solenoids each connected to a separate one of said movable shutter means for selectively opening and closing said shutters.

14. The device of claim 13 wherein said light attenuation means comprises a plurality of adjustable light attenuators positioned within said housing to limit the amount of light transmitted from each of said light emitting portions to the light responsive means.

15. A phototimer adapted for use with a source of X- radiation and an electrical control system for controlling the emission of X-radiation from the source, comprising:

a. fluorescent material for generating a light output in response to incident X-radiation;

b. a light responsive electrical signal generating means adapted for connection to the electrical control system;

c. a light transmitter interposed between said fluorescent material and said light responsive means, said light transmitter defining paths for the transmission of light from separate areas of said material to said light responsive means; and, v d. light interruptor means disposed along selected ones of said paths for selectively blocking the transmission of light from at least one of said areas to said light responsive means.

16. The phototimer of claim 15 wherein said light transmitter includes a plurality of light transmitting panels having light accepting portions adjacent separate ones of said areas.

17. The phototimer of claim 16 additionally including light opaque means interposed between adjacent ones of said panels for preventing the transfer of light between adjacent ones of said panels.

18. The phototimer of claim 16 wherein said panels also have light emitting portions disposed near said light responsive means, and said light interrupter means is interposed between said light emitting portions and said light responsive means.

19. The phototimer of claim 18 wherein said light interruptor means comprises a plurality of light-opaque shields each interposed between a separate one of said light emitting portions and said light responsive means.

20. An X-ray apparatus comprising:

a. a source of X-radiation for emitting a beam of X- radiation along a path;

b. image producing means disposed in the beam path at a position spaced from said source;

c. a phototimer including:

i. fluorescent means positioned within said beam path for generating a light output in response to incident X-radiation;

light responsive electrical signal generating means for generating an electrical signal in response to incident light; iii. light transmitting means interposed between said fluorescent means and said light responsive means and defining paths for the transmission of light from selected areas of said fluorescent means to said light responsive means; and

iv. light interruptor means disposed along selected ones of said light transmission paths for selectively blocking the transmission of light from at least one of said areas to said light responsive means.

21. The X-ray apparatus of claim wherein said light transmitting means includes a plurality of light transmitting panels having light accepting portions near separate ones of said areas and having light emitting portions near said light responsive means, each of said panels defines one of said light transmission paths.

22. The X-ray apparatus of claim 21 wherein said light interruptor means comprises a plurality of movable light opaque shields disposed between said light emitting portions and said light responsive means.

23. An X-ray apparatus comprising:

a. a source of X-radiation for emitting a beam of X- radiation along a path;

b. film cassette positioning means for receiving and positioning an X-ray film cassette within the beam path at a position spaced from said source; and

c. phototiming means comprising:

i. fluorescent means positioned within the beam path at a position between said source and said positioning means for generating a light output in response to incident X-radiation;

ii. light responsive electrical signal generating means positioned out of said beam path for generating an electrical signal in response to incident light;

iii. light transmitting means interposed between said fluorescent means and said light responsive means and defining paths for the transmission of light from selected areas of said fluorescent means to said light responsive means; and,

iv. light interrupter means disposed along selected ones of said light transmission paths for selectively blocking the transmission of light from at least one of said areas to said light responsive means.

24. The X-ray apparatus of claim 23 wherein:

a. said light transmitting means includes a plurality of light transmitting panels each for transmitting light from a different one of said selected areas to said light responsive means; and,

b. said light interrupter means includes movable light-opaque shields positioned along selected ones of said light transmission paths and being movable across their associated paths to selectively block the transmission of light to said light responsive means. 

2. The device of claim 1 wherein said movable shielding means comprises a separate shield for blocking the transmission of light from each one of said light emittting portions to the light responsive means.
 3. The device of claim 2 additionally including shield positioning means for selectively positioning each of said shields to control the transmission of light from said light emitting portions to the light responsive means.
 4. A device for use in combination with an electrical control system including a light responsive signal generating means for controlling an X-ray beam from an X-ray tube source, comprising: a. a fluorescent screen for transforming X-rays into visible light; b. three juxtaposed light transmitting panels each having a light accepting portion adjacent a separate area of said fluorescent screen and having a light emitting portion positioned adjacent the light responsive means for transmitting light to the light responsive means; c. movable shielding means for selectively blocking the transmission of light from said light emitting portions tO the light responsive means; and, d. shield positioning means for selectively positioning said movable shielding means.
 5. The device of claim 4 wherein said movable shielding means includes three shields each adapted to selectively block the transmission of light from a separate one of said light emitting portions to the light responsive means.
 6. The device of claim 5 additionally including adjustable light attenuation means positioned between said light emitting portions and the light responsive means for equalizing the output effect of each of said light emitting portions.
 7. A device for use in combination with a light responsive electrical signal generating means coupled to an electrical control system for controlling an X-ray beam from an X-ray tube source, comprising a. a fluorescent screen for transforming X-rays into visible light; b. a plurality of light transmitting panels each having at least one light accepting portion adjacent a separate area of said fluorescent screen and having a light emitting portion adjacent the light responsive means for transmitting light to the light responsive means; c. movable shielding means for selectively blocking the transmission of light from said light emitting portions to the light responsive means; d. shield positioning means for selectively positioning said movable shielding means; and, e. light attenuation means adapted to equalize the output effect of each of said light emitting portions.
 8. The device of claim 7 additionally including: a. cover means adapted to shield said light transmitting panels such that the only light received by said panels is light emanating from said fluorescent screen; and, b. masking means positioned between said fluorescent screen and said light transmitting panels to limit the transmission of light therebetween to the area of said light accepting portions.
 9. The device of claim 8 wherein said cover means includes: a. a first light-shielding cover positioned adjacent said light receiving panels on the side opposite said masking means; b. a second light-shielding cover positioned adjacent said fluorescent screen on the side opposite said masking means; and, c. a light-shielding peripheral enclosure receiving said first and second covers with said fluorescent screen, said masking means, and said panels sandwiched therebetween.
 10. A device for use in combination with a light responsive electrical signal generating means coupled to an electrical control system for controlling an X-ray beam from an X-ray tube source, comprising: a. an X-ray responsive light generating assembly positioned within the beam of X-rays comprising a fluorescent screen for transforming X-rays into visible light and plurality of light transmitting panels each having at least one light accepting portion adjacent a separate area of said fluorescent screen and having a light emitting portion adjacent the light responsive means for transmitting light to the light responsive means; b. said assembly including masking means positioned between said fluorescent screen and said light transmitting panels to limit the transmission of light therebetween to the area of said light accepting portions; c. movable shielding means for selectively blocking the transmission of light from said light emitting portions to the light responsive means; d. shield positioning means for selectively positioning said movable shielding means; and, e. light attenuation means adapted to equalize the output effect of each of said light emitting portions.
 11. The device of claim 10 wherein said light transmitting panels comprise three panels having abutting edge portions juxtaposed so as to form a contiguous surface, and an opaque substance is interposed between said abutting edge portions to prevent the transmission of light between said panels.
 12. The device of claim 10 wherein said movable shielding means comprises a. a hoUsing surrounding said light responsive electrical control mean, said housing having at least one opening therethrough adjacent said light emitting protions; and b. a plurality of movable shutter means adapted to control the transmission of light from said light emitting portions through said opening to the light responsive means.
 13. The device of claim 12 wherein said shield positioning means comprises a plurality of solenoids each connected to a separate one of said movable shutter means for selectively opening and closing said shutters.
 14. The device of claim 13 wherein said light attenuation means comprises a plurality of adjustable light attenuators positioned within said housing to limit the amount of light transmitted from each of said light emitting portions to the light responsive means.
 15. A phototimer adapted for use with a source of X-radiation and an electrical control system for controlling the emission of X-radiation from the source, comprising: a. fluorescent material for generating a light output in response to incident X-radiation; b. a light responsive electrical signal generating means adapted for connection to the electrical control system; c. a light transmitter interposed between said fluorescent material and said light responsive means, said light transmitter defining paths for the transmission of light from separate areas of said material to said light responsive means; and, d. light interruptor means disposed along selected ones of said paths for selectively blocking the transmission of light from at least one of said areas to said light responsive means.
 16. The phototimer of claim 15 wherein said light transmitter includes a plurality of light transmitting panels having light accepting portions adjacent separate ones of said areas.
 17. The phototimer of claim 16 additionally including light opaque means interposed between adjacent ones of said panels for preventing the transfer of light between adjacent ones of said panels.
 18. The phototimer of claim 16 wherein said panels also have light emitting portions disposed near said light responsive means, and said light interruptor means is interposed between said light emitting portions and said light responsive means.
 19. The phototimer of claim 18 wherein said light interruptor means comprises a plurality of light-opaque shields each interposed between a separate one of said light emitting portions and said light responsive means.
 20. An X-ray apparatus comprising: a. a source of X-radiation for emitting a beam of X-radiation along a path; b. image producing means disposed in the beam path at a position spaced from said source; c. a phototimer including: i. fluorescent means positioned within said beam path for generating a light output in response to incident X-radiation; ii. light responsive electrical signal generating means for generating an electrical signal in response to incident light; iii. light transmitting means interposed between said fluorescent means and said light responsive means and defining paths for the transmission of light from selected areas of said fluorescent means to said light responsive means; and iv. light interruptor means disposed along selected ones of said light transmission paths for selectively blocking the transmission of light from at least one of said areas to said light responsive means.
 21. The X-ray apparatus of claim 20 wherein said light transmitting means includes a plurality of light transmitting panels having light accepting portions near separate ones of said areas and having light emitting portions near said light responsive means, each of said panels defines one of said light transmission paths.
 22. The X-ray apparatus of claim 21 wherein said light interruptor means comprises a plurality of movable light opaque shields disposed between said light emitting portions and said light responsive means.
 23. An X-ray apparatus comprising: a. a source of X-radiation for emitting a beam of X-radiation along a path; b. film cassette positioning means for receiving and positioning an X-ray film cassette within the beam path at a position spaced from said source; and c. phototiming means comprising: i. fluorescent means positioned within the beam path at a position between said source and said positioning means for generating a light output in response to incident X-radiation; ii. light responsive electrical signal generating means positioned out of said beam path for generating an electrical signal in response to incident light; iii. light transmitting means interposed between said fluorescent means and said light responsive means and defining paths for the transmission of light from selected areas of said fluorescent means to said light responsive means; and, iv. light interruptor means disposed along selected ones of said light transmission paths for selectively blocking the transmission of light from at least one of said areas to said light responsive means.
 24. The X-ray apparatus of claim 23 wherein: a. said light transmitting means includes a plurality of light transmitting panels each for transmitting light from a different one of said selected areas to said light responsive means; and, b. said light interruptor means includes movable light-opaque shields positioned along selected ones of said light transmission paths and being movable across their associated paths to selectively block the transmission of light to said light responsive means. 